Jon Paul Burkhart

It's Christmas time and both Marshall and Robin are feeling homesick in New York, and Ted's immature younger sister Heather arrives in the city. Ted has been trying to keep Heather and Barney apart because he fears they will sleep together. Barney and Heather prove Ted wrong and Ted is forced to admit that his sister has grown up.

Brennan and Booth investigate the body of a man murdered for the undisclosed contents of a briefcase; early evidence leads the team to suspect secret operatives are at work, and their theories are supported when the liquefied remains of a CIA agent are discovered in the trunk of a car; meanwhile, Brennan's best-selling book leads to financial success, and serves as a point of contention with Booth; and Jeffersonian intern Wendell loses his scholarship.

Grace has developed a worrying obsession with the aliens, and it threatens Kit's newfound chance at a happy ending when things turn violent. Meanwhile, a deadly new inmate threatens Sister Jude's chance of release from Briarcliff.

Randall adjusts to the foster system, Kate and Toby take the next step in their relationship, Kevin visits Sophie in New York, and Jack and Rebecca finalise Randall's adoption.